Method

Preheat the oven to 180ºC. Grease the inside of a 25cm flan tin with a little of the butter, melting the remainder in a pan over a low heat.

Line the tin with the filo pastry, brushing each sheet with some of the melted butter.

Put the ricotta in a bowl and loosen the texture with a fork. Mix in 100g of the sugar and the egg yolks, followed by the cubes of zest, the grated zest and the chocolate. Mix well together.

In another bowl, beat the egg whites until stiff, then add the remaining sugar. Fold this carefully into the ricotta mixture using a large metal spoon, taking care not to lose the airiness of the whipped whites.

Spread this filling onto the filo pastry on the base of the tin. Brush melted butter over the remaining sheet or sheets of filo. With scissors, cut ribbons of buttered filo pastry and spread these decoratively on the tart.

Bake in the preheated oven for 30 minutes and leave to cool before serving.